A ride height control system for a motor vehicle, in which, in order to control the ride height of the vehicle body, compressed air is pumped to and fro between an accumulator and the air springs using a compressor has been known for a long time from the prior art, for example EP 1 243 447 A2, which is incorporated by reference, and is referred to as a closed ride height control system. In a close ride height control system the air springs are emptied into the accumulator in order to lower the vehicle body, whereas in the case of an open ride height control system the air springs are entered into the atmosphere in order to lower the vehicle body. A closed ride height control system has the advantage over an open ride height control system that rapid raising and lowering of the vehicle body is possible with little expenditure of energy.
A ride height control system has different components for which specific operating parameters have to be complied with for these components not to be damaged. It is therefore possible, in particular, for the compressor and the switchable directional control valves a of a ride height control system to be damaged by excessively high temperatures. It is therefore already known from the prior art to monitor the “compressor temperature” operating parameter and to introduce a switch-off limiting value for this operating parameter. The compressor of the ride height control system is switched off if the compressor temperature reaches the switch-off limiting value, with the result that damage to the compressor is reliably prevented. However, it is to be noted that switching off the sensitive components of the ride height control system when the respective switch-off limiting value is reached either leads to aborting of a current control process or to prohibition of a respective control process in the ride height control system. However, there are control processes which absolutely have to be carried out for safety reasons. In particular, in a motor vehicle with a ride height control system it must always be possible to lower the vehicle body. It can therefore be necessary, for example, to lower the vehicle body from a high height in order to lower the vehicle body to a height which is safe in terms of vehicle movement dynamics or in order to ensure good pedestrian protection in the case of a collision between a motor vehicle and a pedestrian. This is not ensured, for example, if the vehicle body has been raised to the high height shortly before it is lowered using the ride height control system and in this context the operating parameter of a component of the ride height control system has reached the switch-off limit. In this case, the subsequent lowering of the vehicle body would be prohibited. Sufficient lowering of the vehicle body is also not ensured when the lowering process is interrupted prematurely because during the lowering process the operating parameter of a component of the ride height control system reaches the switch-off limit.
DE 19810764 A1, which is incorporated by reference, proposes in this context to operate the compressor in a clocked fashion from the time when the switch-off limiting value for the compressor temperature is reached, with the result that during the clocked operation the compressor does not heat up further and is not damaged. However, it is to be noted that the desired rapid lowering of the vehicle body by emptying the air springs into the compressed air accumulator of the ride height control system is not possible using clocked operation of the compressor.